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Old 10-25-2010, 04:47 PM   #15
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Not sure what you consider and EXTRA wire.

The trailer brakes are 12 volt dc and require a source of power and a ground to each magnet. Normally Airstream brings both functions back from the electric distrubution area with one wire attached to the brake signal form the TV and the brake away switch, the power sources. The second wire is attached to chassis ground.

If you do get dual wire in a common shield make sure there is a polarity strip on the wire so you can maintain polarity within the system.

As long as you bring a power source, one wire, and a ground, as second wire, to each magnet you have completed the circuit.

The suggestion to run #10 wire is to reduce voltage drop across the length of the circuit. Some individuals when rewiring like to bring separate circuits down each side of the trailer thus eliminating the voltage drop to the curb side of the trailer resulting from the wire used to cross from the road side to the curb side. This is over kill if you have up sized the wire to #10.
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Old 06-29-2011, 01:20 PM   #16
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I see this is post is a little old but I thought I would reactivate with a question as follows:

On my new axles the two wires that come out of the backing plate are both white. Does this mean that it does not matter which of the two wires gets the ground connection and which one gets the power from the brake system?

Thanks,

Malcolm
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Old 06-29-2011, 01:29 PM   #17
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Originally Posted by malconium View Post
I see this is post is a little old but I thought I would reactivate with a question as follows:

On my new axles the two wires that come out of the backing plate are both white. Does this mean that it does not matter which of the two wires gets the ground connection and which one gets the power from the brake system?

Thanks,

Malcolm
Malcolm.

Electric brakes do not use any polarized wiring system.

So, you get to chose, however you wish.

Andy
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Old 06-29-2011, 01:54 PM   #18
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Andy,

It does seem a little odd to me that electrically powered magnets would not be polarity sensitive like a solenoid would be but it certainly makes it easier to wire up if I can do it either way.

Thanks,

Malcolm
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Old 06-29-2011, 02:07 PM   #19
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There is no polarity in a DC circuit for parts like magnets, solenoids, light bulbs, ect.

Yes there is polarity in DC electronics with transistors, and IC circuits but not with our stuff
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Old 06-29-2011, 02:27 PM   #20
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Originally Posted by HowieE View Post
There is no polarity in a DC circuit for parts like magnets, solenoids, light bulbs, ect.

Yes there is polarity in DC electronics with transistors, and IC circuits but not with our stuff
I think we are going to have to be careful about the DC polarity for some things in our Airstream.

I am willing to accept that the magnets in my brakes are not sensitive to the DC polarity based on some aspect of how they are placed. I also agree that light bulbs are not polarity sensitive. You are going to have a hard time convincing me though that solenoids are not polarity sensitive. The basic physics of electricity and magnetism says that electromagnetic forces in a coil of wire - which is basically what a solenoid is - is dependent on the direction of current flow. A solenoid pulls or pushes its moveable core in or out depending on the polarity of the DC hookup. In fact AC would not work very well on a solenoid because the direction of the current keeps changing.

I would also expect a typical DC motor to be polarity sensitive. Change the polarity of the connections and it will run in the opposite direction unless it has protective circuitry to prevent that. I notice that the wires on my fresh water pump and my macerator pump are color coded so that they will run in the correct direction. I would bet the DC leads to the refrigerator are too although I have not yet run the wires to it.

The bottom line here - lets not get our DC wires crossed unless we are sure that a given connection is OK with that.

Malcolm
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Old 06-29-2011, 02:30 PM   #21
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Andy,

It does seem a little odd to me that electrically powered magnets would not be polarity sensitive like a solenoid would be but it certainly makes it easier to wire up if I can do it either way.

Thanks,

Malcolm
Malcolm.

I understand what you mean.

Sometimes, some things in life are so simple, that we don't understand it, nor does it make any sense.

Andy
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Old 06-29-2011, 02:34 PM   #22
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For the techies, the direction of current flow through a coil determines which ends become magnetically North and South (Left Hand Rule). For the electric brake magnets, polarity is a non-issue. It is only important that the magnetized coil is attracted to the steel surface of the drum.
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Old 06-29-2011, 06:20 PM   #23
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For the techies, the direction of current flow through a coil determines which ends become magnetically North and South (Left Hand Rule). For the electric brake magnets, polarity is a non-issue. It is only important that the magnetized coil is attracted to the steel surface of the drum.
Is the implication here then that the magnet in the axle is wound in a more or less horseshoe fashion such that both the north and south poles of the resulting magnet point toward the steel surface of the drum?

Malcolm
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Old 06-29-2011, 10:00 PM   #24
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Polarity

You are going to have a hard time convincing me though that solenoids are not polarity sensitive.


Polarity is not an issue with a solenoid. The only issue in automotive type solenoids is that one side is usually already connected to the common side of the circuit. Case in point; a starter solenoid only requires 1 wire to be connected to the coil terminal. When installed in a vehicle, one side of the starter solenoid and one side of the starter motor winding is connected to the common/ground (negative) side of the circuit. The battery positive cable is connected to the starter solenoid (the big bolt) as well as the start wire (small bolt) from the ignition.
If you were to remove the starter from the vehicle and wire it up on the bench and just connect the solenoid wiring to a battery; it would energize regardless of the polarity. As a matter of fact; because the starter motor is a series wound motor, it will run the same direction without regard to the polarity. Where as a parallel wound motor can be reversed, by reversing the polartiy of the armature or the field windings; however if you reverse both the armature and the field simultaneously, the motor will run the same direction as it originally ran.
A lot of motors today are permanant magnet motors and only have one pair of wires to connect. By reversing the polarity on these wires you can reverse the direction of rotation because the polarity of the magnets don't change.
If you want to prove it to yourself. Get a DC relay or a stand alone starter solenoid, like those used on Ford vehicles and wire it up in both polarity senarios. You will see that the relay or solenoid picks up (energizes) either way.
I regards to AC solenoids, there are millions of these solenoids and relays operating machinery in factories all over the country. They are rated in different voltages depending on the application. 120 volt; 240 volt; 480 volt and so on. If you have an air conditioner in your trailer the start and run relays for the compressor are 120 volt AC relays.
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